We have developed an anisotropic random heterogeneous velocity model in methane hydrate-bearing zones, based on the P-wave velocity logs showing a von Karman type autocorrelation function and a bimodal probability distribution function. Synthetic reflection sections with source signals in two different frequency bands imply that the velocity fluctuation of the random model with bimodal distribution causes the frequency dependence of the Bottom Simulating Reflector (BSR) by affecting wave field scattering. A synthetic cross-well section suggests that the strong attenuation observed in field data might be caused by the extrinsic attenuation in scattering. We conclude that random heterogeneity with bimodal probability distribution is a key issue in modelling hydrate-bearing zones, and that it can explain the frequency dependence and scattering observed in seismic sections in such areas.
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